The present invention relates to a glass composition having a low softening point which is used as a bonding material, sealing material, coating material for materials such as ceramics, glass and metal, or as a paste material and the like.
The present invention also relates to a magnetic head suitable for recording and reproducing magnetic information on a magnetic recording medium, and to a sealing glass for bonding a pair of magnetic core halves constituting such a magnetic head.
In various parts used for electronic equipment, different glass materials are used as the materials for bonding, sealing or coating a variety of components each comprising ceramics, glass, metal or the like. These materials are used in various forms such as a bulk, powder, fiber and thin film, either as a material consisting only of glass or as a composite material comprising a glass material and other materials. Also used in a variety of applications is a paste material imparted various functions, which is obtained by mixing a glass material as a glass frit with some other material and a suitable filler, vehicle or the like.
One exemplary application of a glass material in the above-described purpose is a magnetic head, which records and reproduces magnetic information on a magnetic recording medium. In a magnetic head, a glass material is used for bonding a pair of magnetic core halves to form a magnetic gap. Such a glass material is generally called a sealing glass, and represents an important component which exerts influence even on the performance of a magnetic head.
In the following, conventional magnetic heads will be described.
Ferrite is widely used as core materials for magnetic heads because of its superior magnetic property, abrasion resistance, machinability and the like. A magnetic head called a ferrite head is obtained by butting against each other a pair of magnetic core halves each comprising ferrite, at least one of which is formed with a groove for a coil, with a magnetic gap material comprising a non-magnetic material interposed therebetween, and bonding the core halves together with a sealing glass.
Further, with the recent realization of miniaturization and high capacity for magnetic recording and reproducing devices, magnetic recording media having a high coercive force have been increasingly used. As a high-density magnetic head for magnetic recording which is capable of sufficiently writing signals on such media, improved versions of the above-described ferrite head have been developed.
Among them, a magnetic head called a metal in gap (MIG) head is obtained by coating a pair of magnetic core halves at gap-facing surfaces thereof with a magnetic metal film having a high saturation magnetic flux density (e.g., a thin film of a magnetic metal material such as Fexe2x80x94Taxe2x80x94N, Fexe2x80x94Nbxe2x80x94N, Fexe2x80x94Nbxe2x80x94Sixe2x80x94Bxe2x80x94N, Fexe2x80x94Taxe2x80x94C, Coxe2x80x94Taxe2x80x94Zrxe2x80x94Nb or Coxe2x80x94Nbxe2x80x94Zrxe2x80x94N. Hereinafter referred to as xe2x80x9ca magnetic metal film.xe2x80x9d), butting the pair of magnetic core halves against each other with a magnetic gap material interposed therebetween, and bonding the core halves together with a sealing glass.
Also, a magnetic head called a laminated head is obtained by butting each other a pair of magnetic core halves, each of which is constituted by sandwiching a metal magnetic film between non-magnetic substrates, with a magnetic gap material interposed therebetween at the ends of the magnetic metal films of the core halves, and bonding the core halves together with a sealing glass.
In recent years, with the increasing demand for the realization of high performance and high reliability for electronic equipment and various parts, including the above-described magnetic heads, the requirements for the glass materials used in the purpose discussed above have become more severe.
These glass materials need to be subjected to a suitable heat treatment when used, and it is required that a temperature for the heat-treatment be as low as possible in order to prevent materials other than the glass material, parts containing a glass material and equipment containing a glass material from being degraded due to heat. As a glass material in compliance with such requirement, a so-called glass having a low softening point is used.
Meanwhile, the coefficient of thermal expansion of a glass material, in general, tends to increase with a decrease in the softening point of the glass material. Then, in order to prevent a fracture and a crack due to the distortion occurred after cooling, it is required to decrease the coefficient of thermal expansion. Furthermore, in the case of the above-described magnetic heads, for example, it is necessary to control the distortion in order to realize an optimum magnetic recording property and, therefore, glass materials having suitable coefficients of thermal expansion depending on the specifications of the respective magnetic heads are demanded.
Accordingly, these glass materials are required to have suitable temperature characteristic and coefficient of thermal expansion depending on their respective uses. More specifically, glass materials used in the recent electronic equipment and various parts are required to have a working temperature of from 450xc2x0 C. to 650xc2x0 C. and a coefficient of thermal expansion of from 70xc3x9710xe2x88x927 to 130xc3x9710xe2x88x927/xc2x0 C. The working temperature used herein means a temperature at which the viscosity of a glass material becomes 103 Paxc2x7s. Also, the softening point means a temperature determined by the measurement by the testing method JIS R 3104, that is, a temperature at which the viscosity of a glass material becomes 106.6 Paxc2x7s. Except for glass materials exhibiting a special viscosity behavior, the working temperature of a glass material tends to decrease with a decrease in its softening point.
Heretofore, lead glasses of SiO2xe2x80x94B2O3xe2x80x94PbO type, B2O3xe2x80x94PbOxe2x80x94ZnO type and the like have been used as glasses having a low softening point, and the addition of lead has been essential for realizing a low softening point.
However, the conventionally used glasses having a low softening point including lead glasses are not sufficient, especially in terms of water resistance, to be used for the recent electronic equipment and various parts each having even higher performance and higher reliability.
In particular, with the increasing demand for the realization of higher performance and higher reliability, a magnetic head is occasionally exposed to a grinding fluid or the like for a long time during the processing step, resulting in a problem of eroding the sealing glass. In other words, the chemical durability of the sealing glass has often posed problems.
Additionally, the glass materials used in such purpose have been required to be lead-free.
In order to solve the above-described problem in the prior art, it is an object of the present invention to provide a glass composition having a low softening point and an excellent water resistance despite being lead-free. It is another object of the present invention to provide a sealing glass for a magnetic head comprising the above glass composition, and a magnetic head using the same.
In order to solve the foregoing problem, the present invention provides a glass composition containing 0.5 to 14 wt % of SiO2, 3 to 15 wt % of B2O3, 4 to 22 wt % of ZnO, 55 to 90 wt % of Bi2O3, 0 to 4 wt % of Al2O3, 0 to 5 wt % of at least one selected from the group consisting of Li2O, Na2O and K2O. and 0 to 15 wt % of at least one selected from the group consisting of MgO, CaO, SrO and BaO. Herein, the content of each component in the above glass composition was expressed in terms of an oxide.
The present invention also provides a sealing glass for a magnetic head comprising the above glass composition.
The present invention also provides a magnetic head comprising: a magnetic core halves butted against each other with a magnetic gap material interposed therebetween, at least one of which is provided with a groove for a coil; and the above sealing glass for a magnetic head that bonds the core halves.
The present invention further provides a magnetic head comprising: a pair of magnetic core halves butted against each other with a magnetic gap material interposed therebetween at gap-facing surfaces of the core halves, at least one of which is provided with a groove for a coil and at least one of which is formed with a magnetic metal film on the gap-facing surface; and the above sealing glass for a magnetic head that bonds the core halves together.
Further, the present invention provides a magnetic head comprising: a pair of magnetic core halves butted against each other with a magnetic gap material interposed therebetween at ends of magnetic metal films of the core halves, each of which is constituted by sandwiching the magnetic metal film between non-magnetic substrates and at least one of which is provided with a groove for a coil; and the above sealing glass for a magnetic head that bonds the core halves together.